Clinicians and investigators have implicated repetitive trauma and excessive loading of weight bearing articular surfaces as causative factors in degenerative arthritis, but few long-term investigations have supported this data. The purpose of this study is to help delineate the effects of ageing, exercise and excessive load bearing on articular cartilage. Thirty beagle dogs, currently five years of age, have been divided into a control colony and an exercise colony. The control colony has been caged, and the exercise colony run on a treadmill for one hour and fifteen minutes per day, five days per week with jackets weighing approximately 130 percent of the dog's body weight. At regular intervals for the next six years (at ages 5, 7, 9 and 11), two control and three exercise animals will be sacrificed and the hip and knee joints examined by: 1) Roentgenograms; 2) Surface topography of the articular surfaces by gross photographic and scanning electron microscopy; 3) Histologic and histochemical studies of the articular cartilage by staining for glycosaminoglycans, glycoproteins, glycogen, lipids, collagen and elastin; 4) Ultrastructural and cytochemical analysis of the articular surfaces with specific cytochemical stains for lysosomal enzymes, alkaline phosphatase and proteoglycans; 5) Electron microscopic analysis of proteoglycan structure by directly measuring proteoglycan aggregate size; 6) Biochemical and metabolic studies analyzing DNA content, hexosamine content, thymidine incorporation and sulfate incorporation. At the conclusion of the study the investigators will correlate the effects of ageing on articular cartilage and compare these findings to the effects of increased repetitive load bearing. We will then compare the relationships of those parameters to degenerative arthritis of these weight bearing joints.